1,2-Dialkyl-3,5-diphenylpyrazolium salts and their use as herbicidal agents, particularly as herbicidal agents effective for the selective control of wild oats (Avena spp.) in the presence of certain small grains, is disclosed in the Klingsberg et al. Netherlands Application No. 72-17,015, published on June 19, 1973.
Although the 1,2-dialkyl-3,5-diphenylpyrazolium salts in the above-mentioned reference are uniquely effective for selective control of wild oats, said compounds generally exhibit only minimal herbicidal activity against other economically important grass weeds such as barnyardgrass, foxtail and crabgrass.
It would, therefore, be desirable if a compound could be found which would provide selective control of the aforementioned undesirable grasses.
Surprisingly, it has been found that the substitution in the 4- position of the pyrazolium ring in place of hydrogen, particularly by alkoxy, markedly alters the spectrum of postemergence herbicidal activity of the desired pyrazolium compounds. Such alteration changes the biological activity of the latter compounds by providing them with a much broader spectrum of broadleaf weed and of grass control and the most noteworthy changes are seen in the pronounced improvement in Sesbania, mustard, pigweed, morningglory and barnyardgrass control and the selectivity obtained when said compounds are used for grass control in the presence of rice.